Q&A: Biophysicist Philip Nelson on writing a great textbook

If you’ve ever wondered how Rosalind Franklin created her iconic x-ray photo of DNA, how color vision works, or why a butterfly’s wings are iridescent, Philip Nelson’s latest book, From Photon to Neuron: Light, Imaging, Vision (2017), has the answers. The textbook covers the physics and biology of light and discusses optical phenomena from photosynthesis to human vision.

From Photon to Neuron is the University of Pennsylvania professor’s third textbook, following Biological Physics (2004) and Physical Models of Living Systems (2015). In the January issue of Physics Today, Brad Roth calls From Photon to Neuron “a master class” and says the book cements Nelson’s status as “the preeminent author of textbooks at the intersection of physics and biology.”

Physics Today recently caught up with Nelson to talk about his research, the inspiration for his books, and what to do when students don’t understand what you’ve written.

PT: Tell us about your latest textbook. What topics does it cover?

NELSON: I believe that today’s students need to be told what physicists know about light: that it is inherently quantum mechanical in character. That happens right at the beginning of the book, not at the end. To understand how light can form images, we need Richard Feynman’s approach to the probability distribution that governs photons and the idea of stationary phase that underpins it. Once students make that intellectual investment, they are in a position to understand many new techniques such as two-photon imaging. There are also payoffs in areas as diverse as optogenetics and medical imaging. Even “old” topics such as photosynthesis and the photoreceptors in our eyes turn out to require a quantum viewpoint.

PT: What inspires you to write a new textbook?

NELSON: I always look around for a revolution in progress, then ask myself, “Could I get that across to a student? What would I have to cover to get from first-year physics to that destination?” In the case of From Photon to Neuron, I vividly remember the first round of annual conferences after the breakthroughs in superresolution imaging (see Physics Today, December 2014, page 18 ). I had no idea at the time how many other amazing techniques had recently arrived—or were about to arrive—on the scene, but I knew I wanted to distill some of that excitement and give students the information they needed to get out there and participate.

Similarly, my earlier Physical Models of Living Systems emerged from the ongoing revolution in synthetic biology (see the article by Jané Kondev, Physics Today, February 2014, page 31 ).

PT: Reviewers of your books have often remarked on the beautiful photographs and illustrations that accompany the text. How do you choose and develop the artwork?

NELSON: One great thing about the topics I choose is that primary literature articles often have magnificent images. It can be an expensive headache to get the rights to use those images, but it’s worth it, because one of my aims is to make it clear to a student reader that this image embodied a breakthrough. Actually showing the image makes that point more vividly than just describing it. Many scientists have been generous about digging up their original versions and supplying them—even the pre-digital ones.

PT: What has been the most challenging or surprising thing about writing textbooks?

NELSON: Honestly, I never get used to how much rewriting is needed! Luckily, however, I have had the benefit of many sharp students over the years. When they don’t understand what I have written, clearly that’s my fault and must be fixed. A handful of super-readers have also given me deeper help by being able to imagine what I could have done differently. Engaging with all of them has been a constant reminder of my own foolishness, but also a constant joy.

PT: Where do you think the field of biophysics is headed in the next decade?

NELSON: Never prophesize—especially about the future. But seriously, quantitative and physical approaches to living systems are here to stay, and students with such a background will have an “extra sense,” as Charles Darwin put it.

PT: You were one of Sidney Coleman ‘s PhD students in the 1980s. How did you move from theoretical physics to biophysics?

NELSON: It’s been my great good fortune to have colleagues and department chairs who have supported my unpredictable trajectory, and to have outstanding PhD students who were willing to take a chance on me. Throughout this transition, NSF also took the view that interdisciplinary work could be legitimate and even useful, and I’m grateful that they did.

PT: What are you currently reading?

NELSON: Like a lot of people who loved Joseph Polchinski [the University of California, Santa Barbara, theorist who died on 2 February], I am reading his Memories of a Theoretical Physicist, which is available on arXiv .